The present invention relates to a process and an apparatus for converting a solution or suspension into a dried particulate, granulate product.
Pneumatic conveyor dryers (also called "flash dryers") are used for various industrial drying processes. Pneumatic conveyor dryers are described, e.g., in Chemical Engineers' Handbook, fifth edition, McGraw-Hill Book Company, 20-55, and consist of a long tube or duct for carrying a gas at high velocity, a fan or other means to propel the gas, a feeder for addition of the material to be dried and for dispersing such material in the gas stream, and a cyclone or other separation means for separating dried solid particles from the gas. In the usual embodiments of pneumatic conveyor dryers, either the feeder means or the inlet part of the tube or duct comprises means such as grinders, dispersion means, cage mills or rotating paddle means, which will disintegrate particles or particle aggregates fed thereto so that the product being dried will usually have a smaller particle size than the feed. Normally, particles dried in a pneumatic conveyor dryer have a particle size of 50-300 .mu..
It has now been found that a pneumatic conveyor dryer may advantageously be used for a drying process to obtain a dried particulate product of granular character in which, as a total result, the feed material is not disintegrated to a smaller particle size, but rather "built up" and granulated to obtain an end product consisting of discrete particles of larger particle size than is normally produced in a pneumatic conveyor dryer, the final particles consisting of a plurality of single fragments joined together. One interesting embodiment of the process yields a granulate product consisting of particles of a very uniform particle size and of a substantially spherical shape, the particles having a mean particle size of 300-1000 .mu., usually 500-900 .mu.. Such uniform granulate product of the particle size stated and of a free-flowing, non-dusting character, attractive appearance and high bulk density, may be a most useful form of various commercial products, one interesting example being the so-called "single cell protein" materials which may be used, e.g., in animal feed.